Retrospective calculation of radiation dose and improved therapy planning

ABSTRACT

A combined magnetic resonance (MR) and radiation therapy system includes a bore-type magnet with a magnet radiation translucent region which allows radiation beams to travel radially through the magnet and a split-type gradient coil includes a gradient coil radiation translucent region aligned to the magnet radiation translucent region. A radiation source, disposed laterally to the magnet, administers a radiation dose through the magnet and gradient coil radiation translucent regions to an examination region. A dosage unit determines the actual radiation dose delivered to each voxel of a target volume and at least one non-target volume based on a pre-treatment, intra-treatment, and/or post-treatment image representation of the target volume and the at least one non-target volume. A planning processor updates at least one remaining radiation dose of a radiation therapy plan based on the determined actual radiation dose.

This application is a divisional of U.S. patent application Ser. No.13/496,208, filed Mar. 15, 2012, which is a National Stage filing under35 U.S.C. §371(c) of International Application No. PCT/IB2010/054189,filed Sep. 16, 2010, which claims priority to U.S. ProvisionalApplication 61/248,975 filed Oct. 6, 2009, the disclosures of which areincorporated by reference in their entirety.

DESCRIPTION

The present application relates to a method and system for improvedplanning and delivery of radiation therapy. It finds particularapplication to combined magnetic resonance imaging (MRI) andradiotherapy systems capable of simultaneous MR imaging and irradiation,but it may find application in other imaging or spectroscopy modalitiesor other types of treatment.

Radiation therapy is a common therapeutic technique in oncology in whicha dose of high energy gamma (Γ) radiation, particle beam, or otherradiation is delivered to a patient's body to achieve a therapeuticeffect, i.e. eradicate cancerous tissue. The dose is fractionated, orspread out over a period of several weeks, for several reasons. Sincethe radiation beam travels through healthy tissue on its way to thetarget, fractionation allows for the healthy tissue damaged duringtreatments to recover, without allowing the less efficient cancer tissueto repair between fractions.

To minimize unwanted damage while maintaining a therapeutic effect, atherapy plan is generated prior to treatment which details thefractionation schedule along with optimal beam shape and direction.Typically a static volumetric image, e.g. a computed tomography (CT)image, of the tumor and surrounding tissue is acquired. A computerizedplanning system automatically or semi-automatically delineates contoursof the target volume, healthy surrounding tissue, and sensitive areas atrisk of being damaged, such as the spinal cord, glands, or the like,radiation blocking or attenuating tissue, such as bone, etc. Using thecontour data, the planning system then determines an optimal treatmentplan which details the radiation dose distribution and fractionationschedule along with radiation beam direction and shape.

Prior to a radiation treatment, an image, e.g. fluoroscopic, x-ray, orthe like, of the target volume is taken to align the target volumesposition to the radiation therapy coordinate system and to verify theaccuracy of the current therapy plan. The therapy plan can lose accuracyduring the treatment process because of positioning accuracy, day-to-dayvariations in organ position, breathing, heartbeat, increases/decreasesin tumor size, and other physiological processes, e.g. bladder fillingor the like. To account for such uncertainties and achieve the intendedtherapeutic effect, current methods involve irradiating a volumeslightly larger than the target volume determined from the staticvolumetric image. This approach leads to increased damage to healthytissue and can lead to extraneous side effects. If the current therapyplan significantly changes, e.g. if the target volume size has shrunkdue to treatment, it can be cancelled and a new therapy plan isgenerated which can be time-consuming.

The present application provides a new and improved MRI based imageguided radiotherapy dose planning which overcomes the above-referencedproblems and others.

In accordance with one aspect, a method for radiation dose deliveryincludes generating a radiation therapy plan, the radiation therapy planincludes a plurality of radiation doses. A pre-treatment imagerepresentation of a target volume and non-target volumes is acquired anda contour and position of the target volume and at least one non-targetvolume is determined based on the pre-treatment image representation. Aradiation dose including a plurality of radiation beam trajectories andat least one radiation beam geometry is administered. An actualradiation dose delivered to each region of the target volume and the atleast one non-target volume is determined based on their determinedcontours and positions, the radiation beam trajectories and the at leastone radiation beam geometry.

In accordance with another aspect, a magnetic resonance guidedradiotherapy device includes a bore-type magnet which generates a staticmagnetic field in an examination region, the magnet being configuredwith a magnet radiation translucent region which allows radiation beamsto travel radially through the bore-type magnet into a subject disposedtherein. A split-type gradient coil which defines a gap including agradient coil radiation translucent region aligned to the magnetradiation translucent region, the split-type coil being configured toapply selected magnetic field gradient pulses across the imaging region.A radiofrequency (RF) coil is configured to induce and manipulatemagnetic resonance in a subject in the examination region and/or acquiremagnetic resonance data from the examination region. A radiation sourcedisposed laterally to the bore-type magnet, the radiation source beingpositioned to transmit the radiation beams through the magnet andgradient coil radiation translucent regions to an isocenter of thebore-type magnet and a scanner controller which controls the gradientcoil and RF coil to generate an image representation.

One advantage relies in that radiation exposure to healthy tissue isreduced.

Still further advantages of the present invention will be appreciated bythose of ordinary skill in the art upon reading and understanding thefollowing detailed description.

The invention may take form in various components and arrangements ofcomponents, and in various steps and arrangements of steps. The drawingsare only for purposes of illustrating the preferred embodiments and arenot to be construed as limiting the invention.

FIG. 1 is a diagrammatic illustration of a combined magnetic resonance(MR) and radiotherapy system;

FIG. 2 is a flow chart of a method for radiation treatment;

FIG. 3 is a flow chart of another method for radiation dose delivery;

FIG. 4 is a flow chart of another method for radiation dose delivery;

FIG. 5 is a flow chart of another method for radiation dose delivery;and

FIG. 6 is a flow chart of another method for radiation dose delivery.

With reference to FIG. 1, a combined magnetic resonance (MR) andradiotherapy system 10 includes a main magnet 12 which generates atemporally uniform B₀ field through an examination region 14. The mainmagnet can be an annular or bore-type magnet, a C-shaped open magnet,other designs of open magnets, or the like. The magnet includes a magnetradiation translucent region 16 which allows a radiation beam, such asgamma (Γ) rays, x-rays, particle beams, or the like, to pass through themagnet. In one embodiment, the main magnet 12 is a bore-type magnet. Themagnet radiation translucent region 16 is arranged circumferentially toallow the radiation beam to travel radially through an isocenter of thebore. Gradient magnetic field coils 18 disposed adjacent the main magnetserve to generate magnetic field gradients along selected axes relativeto the B₀ magnetic field for spatially encoding magnetic resonancesignals, for producing magnetization-spoiling field gradients, or thelike. The gradient magnetic field coils 18 include a gradient radiationtranslucent region 20 aligned to the magnet radiation translucent region16 to allow the radiation beam to travel through the main magnet 12 andgradient magnetic field coils 18 in a predictable manner to a subject 22in the examination region 14, i.e. the absorption throughout theradiation translucent regions 16, 20 is constant. The magnetic fieldgradient coil 18 may include coil segments configured to producemagnetic field gradients in three orthogonal directions, typicallylongitudinal or z, transverse or x, and vertical or y directions.

The radiation beam originates from a radiation source 24, such as alinear accelerator or the like, disposed laterally to the main magnet 12and adjacent to the radiation translucent regions 16, 20. An absorber 26absorbs any radiation from the source 24 travelling in an unwanteddirection. A collimator 28 helps shaping the beam of radiation tolocalize the treatment to a target volume 30. In one embodiment, thecollimator is an adjustable collimator, such as a multi-leaf collimator(MLC) or the like, which modulates the radiation beam geometry. Theleaves of the MLC allow for conformal shaping of the radiation beam tomatch the shape of the target volume 30 from each angular position ofthe radiation beam around the subject.

A radiation source assembly 32, composed of the radiation source 24, theabsorber 26, and the collimator 28, is mounted on a rail system 34 whichallows the radiation source assembly to be rotated circumferentiallyabout the radiation translucent regions 16, 20 to a plurality ofpositions permitting a corresponding number of radiation beamtrajectories. Alternatively, the radiation source assembly can movecontinuously with its cross section and intensity also modulated on acontinuum. It should be appreciated that other positioning systems ormethods are also contemplated, for example a fixed rail system, anon-fixed rail system, a single rail system, multi-rail system, C-arm,or the like. In one embodiment, the radiation source assembly isrotatable 360° about the bore-type magnet 12; however, in clinicalpractice it is not necessary for such a wide range. In anotherembodiment, a plurality of radiation source assemblies are positionedcircumferentially about the radiation translucent regions 16, 20, eachradiation source assembly having a substantially fixed trajectory. Thisarrangement allows for a reduced radiation therapy session durationwhich may be advantageous to larger or anxious subjects. It should benoted that, the radiation source assembly and rail system can beconstructed from non-ferromagnetic materials so as not to interfere orbe interfered with the main magnet or gradient magnetic field coils.

A radio-frequency (RF) coil assembly 40, such as a whole-body radiofrequency coil, is disposed adjacent to the examination region. The RFcoil assembly generates radio frequency pulses for exciting magneticresonance in aligned dipoles of the subject. The radio frequency coilassembly 40 also serves to detect magnetic resonance signals emanatingfrom the imaging region. The whole body coil can be of a single coil ora plurality of coil elements as part of an array. The RF coil assemblyis configured such that it does not obscure or is radiation translucentadjacent to the radiation translucent regions 16, 20.

To acquire magnetic resonance data of a subject, the subject is placedinside the examination region 14, preferably at or near an isocenter ofthe main magnetic field. A scan controller 42 controls a gradientcontroller 44 which causes the gradient coils to apply the selectedmagnetic field gradient pulses across the imaging region, as may beappropriate to a selected magnetic resonance imaging or spectroscopysequence. The scan controller 42 also controls at least one RFtransmitter 46 which causes the RF coil assembly to generate magneticresonance excitation and manipulation of B₁ pulses. The scan controlleralso controls an RF receiver 48 which is connected to the whole-body orlocal RF coils to receive magnetic resonance signals therefrom.

The received data from the receiver 48 is temporarily stored in a databuffer 50 and processed by a magnetic resonance data processor 52. Themagnetic resonance data processor can perform various functions as areknown in the art, including image reconstruction, magnetic resonancespectroscopy, and the like. Reconstructed magnetic resonance images,spectroscopy readouts, and other processed MR data are stored in animage memory 56 and displayed on a graphic user interface 58. Thegraphic user interface 58 also includes a user input device which aclinician can use for controlling the scan controller 42 to selectscanning sequences and protocols, and the like.

Prior to receiving radiotherapy, a planning processor 60, automaticallyor by user guidance, generates a fractionated radiation therapy plan;each therapy plan includes a plurality of fractions or radiation doses.Each radiation dose includes a prescribed radiation dose, a plurality ofradiation beam trajectories, and at least one radiation beam geometry(cross section). The amount of radiation used in radiotherapy ismeasured in grays (Gy), and varies depending on the type, size, andstage of the tumor being treated. For example, a radiation therapy planwhich mandates a radiation dose of 60 Gy can be fractionated into 30radiation dosage plans of 2 Gy, wherein each radiation dosage plan isadministered five days a week for a total of six weeks. In each session,the radiation is distributed over a plurality of trajectories, e.g. 20,along which the same or varying portions of the session dose isdelivered. Typically, radiation dosage plan for an adult is 1.8-2.0 Gyand 1.5-1.8 Gy for a child.

To determine the radiation beam trajectories and geometry, a detectionunit 62 detects the target volume 30 and non-target volumes, which willbe described in detail later, by determining their contours fromhigh-resolution 3D images by using image processing techniques and/ormodels that describe to volumes. Image processing techniques may includeany combination of automatic or semi-automatic segmentation, edgedetection, principal components analysis, or the like and can becombined with a model that describes the volumes' shape, texture,motion, or the like to further enhance detection. The determinedcontours are stored in memory within the detection unit 62 itself forlater use. In one embodiment, the high resolution 3D imagerepresentation is an MR image representation acquired from the combinedMR and radiotherapy system 10 and is retrieved from the image memory 56for contour delineation. Alternatively, the high resolution 3D imagerepresentation can be acquired using other imaging modalities, e.g.computed tomography (CT), x-ray, x-ray fluoroscopy, ultrasound, or thelike.

The planning processor 60 uses the determined contours to generate theindividual radiation doses and stores them in memory within theprocessor itself. Certain non-target volumes, such as radiation blockingor attenuating tissue and sensitive tissue like tissue, organs, glands,or the like, should avoid receiving radiation. The planning processordetermines beam trajectories which maximize radiation exposure to targetvolume while sparing non-target volumes from unwanted damage.Unfortunately, the position and shape of these volumes can fluctuate ona daily basis due to a number of physiological changes such asbreathing, bladder volume, lung inflation/deflation, weight gain/loss,tumor size, daily variations in organ position, or the like. Instead ofover compensating by irradiating a slightly larger area or generating anew radiation therapy plan altogether, the current radiation therapyplan can be updated by determining the dose delivered to each part ofthe target and non-target volumes after each treatment. A subsequentradiation dose, or all of the subsequent doses, can be altered based onthe delivered radiation dose.

With reference to FIG. 2, in one aspect, after the radiation dose isdelivered, the actual dose delivered to each voxel of the target 30 andnon-target volumes is determined based on a pre-treatment image. Priorto administration of a radiation dose, the scanner controller 42controls the MR system to acquire a 3D pre-treatment imagerepresentation of the target volume 30 and non-target volumes. Thepre-treatment image can be a low-resolution 3D image representation fromwhich the detection unit 62 determines the contours and positions of thetarget volume 30 and the non-target volumes. The planning processor 60aligns the current target volume 30 position to the coordinate system ofthe radiation source assembly 32. Optionally, surgically implantedmarkers and/or landmarks can be used to ease alignment. A radiationcontroller 64 controls the radiation source assembly 32, i.e. itsrotational position, the leaves of the MLC 28, and the radiation source24, to administer treatment at the beam trajectories and geometryaccording to the current radiation dose. After treatment, a dosage unit66 uses the current beam trajectories, current beam geometry, and thedetermined contours and/or positions from the pre-treatment imagerepresentation to determine the actual radiation dose delivered to eachvoxel of the target volume 30 and non-target volumes. The planningprocessor 60 updates the remaining radiation therapy plan, i.e. at leastone or all of the subsequent radiation doses, according to the actualradiation delivered to the target volume 30 and non-target volumes.

With reference to FIG. 3, in a second aspect, after the radiation doseis delivered, the actual dose delivered to each voxel of the target 30and non-target volumes is determined based on a pre-treatment image anda post-treatment image. After the administration of a radiation dose,the scanner controller 42 controls the MR system to acquire apost-treatment image representation of the target volume 30 andnon-target volumes. The detection unit 62 determines the contours andpositions of the target volume 30 and the non-target volumes. The dosageunit 66 determines the actual radiation dose delivered to each voxel ofthe target volume 30 and non-target volumes based on the current beamtrajectories, current beam geometry, and changes of the determinedcontours and/or positions between the pre-treatment and post-treatmentimage representations. By comparing the position of the target 30 andnon-target volumes in the pre-treatment and post-treatment imagerepresentations, the accuracy of the determined actual dose can beimproved. The planning processor 60 updates the remaining radiationtherapy plan, i.e. at least one or all of the subsequent radiationdoses, according to the actual radiation delivered to the target volume30 and non-target volumes.

With reference to FIG. 4, in a third aspect, after the radiation dose isdelivered, the actual dose delivered to each voxel of the target 30 andnon-target volumes is determined based on a pre-treatment image and amotion model. Prior to administration of a radiation dose, the scannercontroller 42 controls the MR system to acquire a 3D pre-treatment imagerepresentation of the target volume 30 and non-target volumes andacquire a motion signal from an external sensor 68, e.g. a respiratorysensor, ECG sensor, or the like. The detection unit 62 determines thecontours and positions of the target volume 30 and the non-targetvolumes and determines parameters for the motion model based on thesignal from the external sensor. The motion model predicts the target 30and non-target volumes' positions during treatment. The planningprocessor 60 aligns the current target volume 30 position to thecoordinate system of the radiation source assembly 32. Optionally,surgically implanted markers and/or landmarks can be used to simplifyalignment. The radiation controller 64 controls the radiation sourceassembly 32, i.e. its rotational position, the leaves of the MLC 28, andthe radiation source 24, to administer treatment at the beamtrajectories and geometry according to the current radiation dose. Aftertreatment, the dosage unit 66 uses the current beam trajectories,current beam geometry, and the determined contours and/or positions fromthe pre-treatment image representation and the determined motion modelto determine the actual radiation dose delivered to each voxel of thetarget volume 30 and non-target volumes. By predicting the target 30 andnon-target volumes' positions during treatment, the accuracy of thedetermined actual dose can be improved. The planning processor 60updates the remaining radiation therapy plan, i.e. at least one or allof the subsequent radiation doses, according to the actual radiationdelivered to the target volume 30 and non-target volumes.

With reference to FIG. 5, in a fourth aspect, after the radiation doseis delivered, the actual dose delivered to each voxel of the target 30and non-target volumes is determined based on a pre-treatment image anda plurality of 3D intra-treatment images. Prior to administration of theradiation dose, the scanner controller 42 controls the combined MR andradiotherapy system 10 to acquire a 3D pre-treatment imagerepresentation of the target volume 30 and non-target volumes. Thedetection unit 62 determines the contours and positions of the targetvolume 30 and the non-target volumes from which the planning processor60 aligns the current target volume 30 position to the coordinate systemof the radiation source assembly 32. Optionally, surgically implantedmarkers and/or landmarks can be used to simplify alignment. A radiationcontroller 64 controls the radiation source assembly 32, i.e. itsrotational position, the leaves of the MLC 28, and the radiation source24, to administer treatment at the beam trajectories and geometryaccording to the current radiation dose. During the treatment, thescanner controller 42 controls the combined MR and radiotherapy system10 to acquire a plurality of 3D intra-treatment image representations ofthe target volume 30 and the non-target volumes. After treatment, thedetection unit 62 determines the contours and positions of the targetvolume 30 and the non-target volumes from the intra-treatment imagerepresentations. The dosage unit 66 uses the current beam trajectories,current beam geometry, and the determined contours and/or positions fromthe pre-treatment and intra-treatment image representations to determinethe actual radiation dose delivered to each voxel of the target volume30 and non-target volumes. By periodically monitoring the actualposition of the target volume 30 and the non-target volumes duringtreatment, the accuracy of the determined actual dose can be improved.The slower time-scale of the 3D intra-treatment image representation canaccount for respiratory motion. The planning processor 60 updates theremaining radiation therapy plan, i.e. at least one or all of thesubsequent radiation doses, according to the actual radiation deliveredto the target volume 30 and non-target volumes.

With reference to FIG. 6, in a fifth aspect, after the radiation dose isdelivered, the actual dose delivered to each voxel of the target 30 andnon-target volumes is determined based on a pre-treatment image and aplurality of 2D/1D intra-treatment images. The shorter time intervalbetween 2D intra-treatment images and even shorter time interval between1D navigator pulses can account for faster pulsatile motion of thevolumes. Prior to administration of the radiation dose, the scannercontroller 42 controls the combined MR and radiotherapy system 10 toacquire a 3D pre-treatment image representation of the target volume 30and non-target volumes. The detection unit 62 determines the contoursand positions of the target volume 30 and the non-target volumes fromwhich the planning processor 60 aligns the current target volume 30position to the coordinate system of the radiation source assembly 32.Optionally, surgically implanted markers and/or landmarks can be used tosimplify alignment. A radiation controller 64 controls the radiationsource assembly 32, i.e. its rotational position, the leaves of the MLC28, and the radiation source 24, to administer treatment at the beamtrajectories and geometry according to the current radiation dose.During the treatment, the scanner controller 42 controls the combined MRand radiotherapy system 10 to acquire a plurality of 2D/1Dintra-treatment image representations of the target volume 30 and thenon-target volumes. After treatment, the detection unit 62 determinesthe contours and positions of the target volume 30 and the non-targetvolumes from the 2D/1D intra-treatment image representations. The dosageunit 66 uses the current beam trajectories, current beam geometry, andthe determined contours and/or positions from the pre-treatment andintra-treatment image representations to determine the actual radiationdose delivered to each voxel of the target volume 30 and non-targetvolumes. By monitoring the actual position of the target volume 30 andthe non-target volumes during treatment at a higher time resolution, theaccuracy of the determined actual dose can be improved. The planningprocessor 60 updates the remaining radiation therapy plan, i.e. at leastone or all of the subsequent radiation doses, according to the actualradiation delivered to the target volume 30 and non-target volumes.Alternatively, the detection unit 62 determines a motion model based onthe 2D/1D intra-treatment image representations and the motion model isused to determine the actual radiation dose.

In one embodiment, the planning processor 60 updates the remainingradiation therapy plan, i.e. at least one or all of the subsequentradiation doses, automatically. In another embodiment, the radiationplan is updated under user guidance, e.g. by a physician or clinician.The physician verifies the detection of the contours and positions ofthe target 30 and non-target volumes on the graphic user interface 58.The high resolution image representation used in determining the therapyplan, pre-treatment image representations, intra-treatment imagerepresentations, and post-treatment image representations are displayedon the graphic user interface 58 with the contours and positions ofvolumes delineated. Using the input device, the physician can identifythe target volume 30 and non-target volumes, i.e. sensitive tissue,organs, or the like.

In another embodiment, the planning processor 60 registers all imagerepresentations of the target 30 and non-target volumes and displays theregistered image representations on the graphic user interface 58 forevaluation by a physician. Based on changes to the volumes throughouttime points during the therapy plan, the physician can then choosewhether to proceed with the current therapy plan, update the remainingradiation doses of the therapy plan, or cancel the therapy plan.Alternatively, the planning processor 60 displays the actual radiationdose delivered to each voxel of the target volume 30 and non-targetvolumes as an intensity of color map registered to one of the highresolution image representation used in determining the therapy plan,pre-treatment image representations, intra-treatment imagerepresentations, or post-treatment image representations for evaluationby the physician.

In another embodiment, a contrast-enhancing agent, e.g. gadolinium (Gd)based, super-paramagnetic iron oxide (SPIO) and ultra-small SPIO (USPIO)based, manganese (Mn) based, or the like, is introduced into the subject22 to improve contrast of MR image representations. A contrast enhancingagent can improve contour detection and model parameter accuracy. Thecontrast enhancing agent is administered prior to acquiring ahigh-resolution, volumetric image representation for generating aradiation therapy plan and is administered prior to acquiring apre-treatment image representation for updating the radiation therapyplan.

The invention has been described with reference to the preferredembodiments. Modifications and alterations may occur to others uponreading and understanding the preceding detailed description. It isintended that the invention be constructed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims or the equivalents thereof.

The invention claimed is:
 1. A computer-implemented method for radiationdose delivery, the method comprising: generating, by a processor, aradiation therapy plan, wherein the radiation therapy plan includes aplurality of radiation doses; acquiring, by the processor, apre-treatment 3D image representation of a target volume and non-targetvolumes; determining, by the processor, a contour and position of thetarget volume and at least one non-target volume based on thepre-treatment image representation; by the processor, controlling aradiation therapy apparatus to deliver the radiation dose, wherein theradiation dose includes a plurality of radiation beam trajectories andat least one radiation beam geometry; during administering the radiationdose, with the processor, controlling a magnetic resonance diagnosticimaging device to generate 2D intra-treatment image representations and1D navigator pulses; and determining, by the processor, an actualradiation dose delivered to each region of the target volume and the atleast one non-target volume based on the pre-treatment imagerepresentation, the 2D intra-treatment image representations, and the 1Dnavigator pulses, the radiation beam trajectories, and the at least oneradiation beam geometry.
 2. The method according to claim 1, furtherincluding: with the processor, acquiring a motion model and using themotion model in determining the actual dose delivered to each region. 3.The method according to claim 1, further including: during administeringthe radiation dose, with the processor, updating at least one remainingradiation dose of the generated radiation therapy plan based on thedetermined actual radiation dose.
 4. The method according to claim 1,further including: after administering the radiation dose, controllingthe magnetic resonance diagnostic imaging apparatus to acquire a 3Dpost-treatment image representation of the target volume and the atleast one non-target volume; determining a contour and position of thetarget volume and at least one non-target volume based on thepre-treatment 3D image representation, the 2D intra-treatment imagerepresentations, the 1D navigator pulses, and the post-treatment 3Dimage representation; and determining the actual radiation dosedelivered to each region of the target volume and the at least onenon-target volume based on their determined contours and positions fromthe pre-treatment and post-treatment 3D image representations and the 2Dintra-treatment image representations, the 1D navigator pulses, theradiation beam trajectories, and the at least one radiation beamgeometry.
 5. The method according to claim 1, further including:acquiring a motion signal from an external sensor during administeringthe radiation dose; determining a motion model based on contours andpositions of the target volume and at least one non-target volumedetermined from the pre-treatment 3D image representation and theacquired motion signal; and determining the actual radiation dosedelivered to each region of the target volume and the at least onenon-target volume based on their determined contours and positions, theradiation beam trajectories, the at least one radiation beam geometry,the determined motion model, and the 2D image representations, the 1Dnavigator pulses.
 6. The method according to claim 5 further including:prior to acquiring the 3D pre-treatment image representation, surgicallyimplanting markers.
 7. The method according to claim 1, furtherincluding: acquiring a motion signal from an external sensor during theadministration of the radiation dose, acquiring a plurality of the 2Dintra-treatment image representations of a target volume and non-targetvolumes; acquiring a motion model; and determining the actual radiationdose delivered to each region of the target volume and the at least onenon-target volume based on their contours and positions determined fromthe pre-treatment image representation, the motion model, the 2D imagerepresentations, the 1D navigator pulses, the radiation beamtrajectories, and the at least one radiation beam geometry.
 8. Themethod according to claim 1, further including: acquiring at least oneof a three-dimensional (3D) intra-treatment image representation of thetarget volume and at least one non-target volume.
 9. The methodaccording to claim 1, wherein the step of updating the at least oneremaining radiation dose is performed automatically orsemi-automatically.
 10. The method according to claim 1, furtherincluding: displaying a representation of the actual radiation dosedelivered to each voxel of the target volume and non-target volumes. 11.A non-transitory computer-readable medium carrying software configuredto control one or more processors to perform the method according toclaim
 1. 12. The method according to claim 1, further including: priorto acquiring the pre-treatment 3D image representation, introducing acontrast agent into a patient to be treated.
 13. A magnetic resonanceguided radiotherapy device comprising: a magnetic resonance imagingsystem configured to image a subject; a radiotherapy device configuredto deliver radiation to the subject; and one or more processorsconfigured to perform the method according to claim
 1. 14. The magneticresonance guided radiotherapy device according to claim 13, wherein themagnetic resonance imaging system includes a split bore type magnetwhich defines a gap defining a radio translucent region, theradiotherapy device configured to deliver the radiation doses to thesubject through the radio translucent region.
 15. The method accordingto claim 1, wherein the magnetic resonance diagnostic imaging deviceincludes a split bore defining a radio translucent region through whichthe radiation doses are delivered.